Branched polyolefin synthesis

ABSTRACT

This invention relates to a process for the synthesis of addition polymers containing branches upon branches and having a polymerizable olefin end group by a convenient one-pot polymerization of selected vinyl monomers with chain polymerization initiators and a method to provide olefinic end groups by chain termination agents; and polymers produced thereby characterized by branch-on-branch structure and lower inherent viscosity than heretofore possible.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. application Ser. No.09/462,969, filed Jan. 14, 2000, allowed on Oct. 10, 2002 now U.S. Pat.No. 6,518,383 which claims the benefit of U.S. Provisional ApplicationNo. 60/052,859, filed Jul. 17, 1997.

BACKGROUND OF THE INVENTION

Macromolecular engineering using commodity monomers is becoming a majortrend in polymer technology to satisfy the demand for new properties,improved cost effectiveness, ecology and quality. Functional polymerswith low molecular weight, low polydispersity, compact, branchedstructures and terminally-located reactive groups are expected toexhibit superior performance/cost characteristics, by virtue of lowerinherent viscosity and higher reactivity vs. conventional linearstatistical copolymers.

The terminally-functional branched polymers appear to be ultimatereactive substrates for networks, because the branch points cansubstitute for a significant portion of expensive reactive groups andprovide better distribution of the reactive groups. Polymers havinglarge numbers of short branches below critical molecular weight areunlikely to form any entanglements and should exhibit low inherentviscosity and good flow even in concentrated solutions.

Conventional techniques for synthesizing well-defined branched polymersrequire expensive multistep processes involving isolation of reactiveintermediate macromonomers. The macromonomers have polymerizable endgroups, which are usually introduced using functional initiator,terminating or chain transfer agent. Well-defined branched polymers areprepared by the macromonomer homopolymerization or copolymerization withsuitable low molecular weight comonomer selected based on knownreactivity ratios. These methods have been reviewed and onlysingle-branch polymers from single incorporation of the macromonomersare reported; multiple reincorporation of the growing macromonomers wasnever attempted, e.g., R. Milkovich, et al., U.S. Pat. No.3,786,116; P.Remp, et al., Advan. Polymer Sci., 58, 1 (1984); J. C. Salamone, ed.,Polymeric Materials Encyclopedia, Vol.3 and 4 (1996).

Several linear macromonomers were prepared by end-capping of livinganionic polyolefins with unsaturated terminating agents providingpolymerizable olefin end-groups, e.g., R. Asami et al., Macromolecules,16, 628 (1983). Certain macromonomers have been incorporated into simplegraft polymers by homo- or copolymerization with branched structure notwell-characterized and reincorporation of the macromonomers into morecomplex structures was not considered.

Dendrimers or hyperbranched polymers are conventionally prepared usingexpensive, special multifunctional monomers or expensive multistepmethods requiring repetitive isolation of the reactive intermediates.Nothing in the prior art discloses synthetic conditions for productionof macromonomers or polymers containing branches upon branches.

SUMMARY OF THE INVENTION

This invention relates to a general process for the synthesis ofpolyolefins containing branches upon branches and having polymerizableolefin end groups by a convenient one-pot polymerization of selectedvinyl monomers with chain polymerization initiators and a method toprovide olefin end groups by chain termination agents. Thepolymerization is carried out in such a manner that chain terminationoccurs gradually and each chain termination event terminates thatparticular polymer chain with polymerizable olefinic functionality.Subsequent reincorporation of the linear polymer chains produced earlyin the reaction leads to branching of subsequently-formed macromoleculeswhich are terminated with polymerizable olefinic functionality.Subsequent reincorporation of the branched macromolecules leads tosubsequently-formed polymer molecules containing branches upon brancheswhich are terminated with polymerizable olefinic functionality.Spontaneous repetition of the process leads to highly branched orhyperbranched dendritic products still retaining polymerizable olefinictermini.

This invention concerns an improved process for the anionicpolymerization of at least one vinylic monomer to form a branchedpolymer comprising contacting, in the presence of an anionic initiator:

(i) one or more anionically polymerizable vinylic monomers having theformula CH₂═CYZ, and

(ii) an anionic polymerization chain terminating agent of formulaCH₂═CZ—Q—X, wherein:

Q is selected from the group consisting of a covalent bond, —R′—,—C(O)—, and —R′—C(O)—;

Y is selected from the group consisting of R, CO₂R, CN, and NR₂;

X is selected from the group consisting of halogen, and RSO₃;

Z is selected from the group consisting H, R, and CN;

R is selected from the group consisting of unsubstituted and substitutedalkyl, vinyl, aryl, aralkyl, alkaryl and organosilanyl groups and R′isselected from the group consisting of substituted or unsubstitutedalkylene, arylene, aralkylene, alkarylene and organosilanylene groups;the substituents being the same or different and selected from the groupconsisting of carboxylic acid, carboxylic ester, hydroxyl, alkoxy andamino; wherein the improvement comprises obtaining higher yields ofbranched polymer, the polymer having dense branch upon brancharchitecture and polymerizable vinylic chain termini, employing steps I,III, VI and at least one of II, IV and V:

I. reacting (i) with an anionic initiator in a first step:

II. decreasing the ratio of (i) to anionic initiator toward 1;

III. adding (ii) optionally with some (i) in a second step;

IV. selecting the rate of the (ii) addition, dependent on the (ii)reactivity;

V. increasing the ratio of (ii) to anionic initiator toward 1; and

VI. increasing the conversion of (i), (ii) and olefinic end groups from70 to 100%.

Based on the disclosure and Examples presented herein, one skilled inthe art can select the optimum steps I-VII with minimum experimentation.One skilled in the art will also be able to select the appropriateanionic initiator and chain transfer agent for the monomer(s) beingpolymerized, by reference to the well-known conditions for anionicpolymerization. Optionally, the process includes the step, VII, ofconverting anionic-growing end groups into non-polymerizable end groups.It is preferred to operate process step V at a ratio of about 0.7 to 1,most preferably from 0.8 to 1. In step IV, the rate of addition willvary in the same direction as reactivity of (ii) so that addition willbe relatively slow for less reactive component (ii) and will increasecommensurate with increased reactivity of component (ii).

This invention further concerns the product of the above reaction whichis composed primarily of a polymer having a branch-upon-branch structureand a polymerizable olefinic end group, having the structure:

B′=Y, B;

m=1 to 100, preferably 1 to 20, more preferably 1 to 10; n =0 to 100,preferably 0 to 50, more preferably 1 to 20; p=0 to 100, preferably 0 to50, more preferably 1 to 20; and n+m+p>2, preferably 5 to 50, morepreferably 5 to 20;

if m>1, then the m insertions are consecutive or not consecutive;

A=anionic initiator moiety selected from the group consisting of R; and

Q, Y, Z are as earlier defined.

More particulray, A=butyl, Z=H, and Y=Ph, Q=C₆H₄CH₂. W is CZ═CH₂, acomposition of claim 10 wherein W is a non-polymerizable moiety, or H.

Branch-upon-branch polymers (BUBP) are superior over straight branchpolymers (SBP) in terms of more compact structure, reflected in lowerinherent viscosity and better flow properties in melts and solutions forany given molecular weight of polymers. Therefore, BUBPs require lesssolvents and lower temperature than SBPs for processing.

BUBPs with terminal end groups are superior over SBP substrates byhaving much larger network fragments, which can be preformed andincorporated into new topology networks. BUBPs allow formation of newtypes of hybrid networks by combining different BUBPs with a goodcontrol on molecular level.

BUBPs allow incorporation of larger numbers of branch points permacromolecule, which are equivalent to curing sites. This improveseconomy and conversion of reactive coatings by reducing the number ofexpensive curing sites.

In general, BUBPs offer at least a 10 percent improvement over SBPs ofthe same molecular weight in such characteristics as lower viscosity,reduced need for solvent, fewer curing sites in reactive substrates fornetworks and higher conversion of curing sites in final coatings, all ofwhich provide better product stability.

DETAILS OF THE INVENTION

We have discovered a process for the synthesis of polyolefins containingbranches upon branches and having polymerizable olefin end groups by aconvenient one-pot polymerization of selected vinyl monomers with chainpolymerization initiators and a method to provide olefin end groups bychain-termination agents. The polymerization is carried out in such amanner that chain termination occurs gradually and eachchain-termination event terminates that particular polymer chain withpolymerizable olefinic functionality. The process is shown in Scheme 1.

Subsequent incorporation of the linear polymer chains 1 produced earlyin the reaction leads to branching of subsequently-formed macromoleculesterminated with polymerizable olefinic functionality 2. Subsequentreincorporation of the branched macromolecules 2 leads to polymermolecules containing branches upon branches 3 which are terminated withpolymerizable olefinic functionality. Spontaneous repetition of theprocess leads to highly branched or hyperbranched dendritic productsstill retaining polymerizable olefinic termini.

The polymers made by the present process are useful in a wide variety ofapplications including coatings, processing aids in extrusion, cast,blown or spray applications in fiber, film, sheet, composite materials,multilayer coatings, photopolymerizable materials, photoresists, surfaceactive agents, dispersants, adhesives, adhesion promotors,compatibilizers and others. End products taking advantage of availablecharacteristics, particularly low inherent viscosity, can includeautomotive and architectural coatings having high solids, aqueous- orsolvent-based finishes.

In a preferred process, the anionic initiator is selected from alkalimetals, radical anions, alkyllithium and other organometallic initiatingcompounds, ester enolates, functionalized initiators, typical examplesof which include: butyl-, methyl-, isopropyl-, phenyl-, vinyl-,allyl-lithiums, cumyl potassium, fluorenyl lithium.

Chain termination agents include p-vinylbenzyl chloride and bromide,p-vinylbenzyl tosylate, allyl chloride and bromide,vinyldimethylchlorosilane, vinyl(chloromethyl)dimethylsilane,p-vinylphenyldimethylchlorosilane, methacryloyl chloride.

Substituents Q and X of the chain terminating agent are chosen to conveythe appropriate reactivity in the terminating step and in anioniccopolymerization of the desired monomer(s) under polymerizationconditions.

The process can be conducted by bulk, solution, suspension or emulsionpolymerization using batch or preferably starved feed reactor, whichoffers better process control.

The treelike dendritic branched polymers are formed by in situgeneration and copolymerization of first linear and subsequentlyincreasingly branched macromonomers through the polymerizable olefingroup (Scheme 1). The method can be employed in anionic polymerizationof styrene initiated by alkyllithiums, where dendritic structures areformed by continuous addition of vinylbenzyl halides and/orvinylchlorosilanes acting as chain terminating/functionalizing/branchingagents (Scheme 2). The data are consistent with a mechanism, in whichthe initially-formed linear macromolecules receive predominantly thevinyl end group through the termination by the vinylbenzylhalide orvinylchlorosilane. The vinyl reactive end group allows the linearmacromonomer to participate in analogous subsequent (secondary)copolymerization steps leading eventually to even more branchedstructures (“branch upon branch” or dendrigrafts).

Polystyrenes with molecular weights in the range 3,000-60,000,polydispersity <2.5 with 5 to 40 branches, each containing 3 to 30monomer units were prepared, primarily controlled by theinitiator/monomer/chain terminating agent ratio, relative additionrates, the reactivity ratios of the macromonomer and (co)monomers.

A chain polymerization is controlled by a chain termination step so asto provide a polymerizable olefin end group (Scheme 1). The branch uponbranch structure is build by in situ generation and copolymerization oflinear and subsequently increasingly branched macromonomers through thepolymerizable olefinic group.

The monomer copolymerizability of CH₂═CYZ primarily determined by thesteric and electronic properties is well documented in the art. Thechain process can involve either one or several different comonomers andis preferably anionic but can also be cationic or radical. Typicalmonomers include monoolefins, preferably styrene, a-methyl styrene,substituted styrenes, substituted styrenes with protected functionalgroups, vinyl aromatics, vinylpyridines, conjugated dienes, vinylsilanes, acrylates, methacrylates, acrylonitrile, vinylidene cyanide,alkyl cyanoacrylates, methacrylonitrile, vinyl phenyl sulfoxide, vinylaldehydes, vinyl ketones and nitroethylenes.

The data are consistent with a mechanism, in which the initially-formedbranched macromolecules 2 receive predominantly the olefin end groupthrough the chain termination. See Scheme 1. Having a reactive olefinend group allows 2 to participate in analogous subsequent (secondary)copolymerization steps leading eventually to branch-upon-branchpolymers, 3.

Formation of branch-upon-branch structures 3 is indicated by thesignificant increase (up to 50 ×) in the polymer molecular weightcompared to the control experiments where the same monomer/initiatorratios but nonolefin chain terminating agents such as benzyl chloride ormethanol are used instead of the p-vinylbenzyl chloride.

In general, vinylsilane terminated macromonomers show much lowerreactivities toward homo- and co-polymerizations under the conditionsstudied, leading to polymers with lower molecular weight and lessbranched structures.

Branched structures of copolymers 3 are confirmed by very low inherentviscosities, values of “a” coefficient in Mark-Houwink equation, [η]=KM_(a), falling in the range 0.18-0.66 vs. 0.72 for linear polystyrenes,branching factors approaching 0.4 and the RMS radius less than a half ofthe linear analog of the same molecular weight in the range 10₅-10₆ asmeasured by GPC with a dual RI/LS detector.

EXAMPLES 1 TO 41

Preparation of Branch-Upon-Branch Polystyrenes Using p-VinylbenzylChloride as Chain-Terminating Agent

The procedure of Scheme 2 illustrates the preparation and analysis ofthe branch-upon-branch polymer architecture by a multi-step/one-potprocess. Formation of the branch-upon-branch architecture is determinedby type of monomer and chain terminating agent (CTA), and by initiatorconcentration and rate of monomer and CTA addition. The expression “Ph”is used as an abbreviation for phenyl, “PSt” as an abbreviation forpolystyrene and “PhMe” is an abbreviation for toluene.

EXAMPLE 1

Polymerization of Styrene with p-Vinylbenzyl Chloride as aChain-Terminating Agent

Part Ingredient Amount I THF 10 ml styrene 2 g II BuLi (2.0 M in hexane)1 g III p-vinylbenzyl chloride 0.25 g styrene 0.75 g

Part I was charged into the dry reactor equipped with a magnetic stirrerand nitrogen-positive pressure, and cooled to −78° C. in a dryice/acetone mixture in a dry-box. After 15 min., Part II (BuLi) wasadded at once and the reactor contents were held at −78° C. for anadditional 20 minutes. Then, Part III was fed gradually over 5 min. Thereactor contents were held at −78° C. for an additional 35 minutes.About 0.5 g of sample was withdrawn followed by GC determination of thestyrene and p-vinylbenzyl chloride concentrations. Volatiles werestripped on a rotovap. The polymer was dissolved in methylene chloride,filtered through a silica and volatiles were stripped on high vacuum forseveral hours and the oligomers/polymers were analyzed by NMR and GPC.Yield 3.0 g, Mn=31,600, Mw/Mn=2.37 vs. linear PSty in tetrahydrofuran(THF) by GPC. Decane was used as an internal GC standard and molarresponse factors were determined using mixtures of known compositioncontaining styrene, p-vinylbenzyl chloride and decane. Polymercomposition was followed by Matrix Assisted Laser Desorption Ionization(MALDI) Mass Spectroscopy. Polymer molecular weight was measured by GPCusing RI, LS and viscosity detectors. Structure of the polymers,including branching density and end groups, was characterized (seeExamples 42 to 46) by ¹H and ¹³C NMR, MALDI, light scattering, GPC withdual RI/capillary viscometry and RI/LS detectors.

EXAMPLES 2 TO 11

Synthesis of dentritic polystyrenes from BuLi, styrene, vinylbenzylchloride (VBC), and linear analogs using either benzyl chloride (BC) orbenzyl bromide (BB) in cyclohexanes (CHE), THF or in toluene at roomtemperature. M_(n) and M_(w)/M_(n) by GPC in THF vs. PSty standards;styrene added at once to BuLi/THF in the 1^(st) step; and commercialgrade substrates used without purification. See Table 1 for results.

TABLE 1 BuLi Sty (mmol) M_(w)/M_(n) M_(n)/th.^(a)) Example (mmol)(1^(st) + 2^(nd) steps) CTA (mmol) Solvent (ml) M_(n) (GPC) (GPC) linearTg (° C.) Yield (g) 2 3.040 1.92 1.97 (VBC) 1.1 CHE   17,000 2.39 2400.14 3 0.912 28.8 + 1.92 0.655 (VBC)  5 THF 31,700 2.38 3.680 90 2.8 46.080 3.84 5.24 (VBC) 1 THF 19,300 2.11 240 0.1 5 3.040 19.2 + 1.92 1.97(VBC) 5 THF 13,900 4.70 898 73 2.6 6 3.040 19.2 + 1.92 2.37 (BC)  5 THF12,800 2.65 871 71 2.5 7 0.912 1.92 0.655 (VBC)  3 PhMe 6,600 3.86 3930.16 8 3.040 19.2 + 1.92 1.97 (VBC) 5 PhMe 12,900 3.46 898 72 2.6 96.080 19.2 + 5.76 3.93 (VBC) 5 PhMe 17,200 5.01 602 74 2.1 10 9.1219.2 + 9.60 6.55 (VBC) 5 PhMe 7,800 5.51 503 55 1.1 11 9.12 19.2 + 9.607.90 (BC)  5 PhMe 5,700 1.36 476 53 2.3 ^(a))M_(n)th= Sty(g)/BuLi(mole) + 57 + MW (CTA) − MW (halogen)

EXAMPLES 12 to 31

Synthesis of dentritic polystyrenes from BuLi, styrene, vinylbenzylchloride (VBC), vinylbenzyl bromide (VBB), and linear analogs usingeither benzyl chloride (BC) or benzyl bromide (BB), or methanol in THFat −78° C. M_(n) and M_(w)/M_(n) by GPC in THF vs. PSty standards; BuLiadded at once to styrene/solvent in the 1^(st) step; and commercialgrade substrates were dried over molecular sieves. See Table 2 forresults.

TABLE 2 BuLi Sty (mmol) M_(w)/M_(n) Tg Example (mmol) (1^(st) + 2^(nd)steps) CTA (mmol) THF (ml) M_(n) (GPC) (GPC) M_(n)/th.^(a)) (° C.) Yield(g) 12^(b)) 3.04 19.2 + 5.76 1.97 (VBC) 5 31,300 4.23 1,029 88 2.613^(b)) 3.04 19.2 + 5.76 2.37 (BC) 5 5,800 2.84 1,002 33 2.9 14^(b))3.04 19.2 + 5.76 1.64 (VBC) 5 48,100 5.67 1,029 95 2.7 15^(b)) 3.04 19.29.38 (MeOH) 10 3,400 2.76 743 47 2.1 16 3.04 19.2 1.97 (BC) 10 3,7002.83 832 58 2.1 17 3.04 19.2 1.64 (VBC) 10 23,300 1.93 859 89 2.2 183.04 19.2 + 7.20 1.64 (VBC) 10 31,600 2.37 1,079 88 3.0 19 3.0 32.1 +19.2 2.29 (VBC) 13.3 37,900 1.93 1,954 93 4.0 20 3.0 32.1 + 28.8 2.62(VBC) 13.3 42,900 3.08 2,287 94 5.8 21 3.0  3.5 + 38.4 2.62 (VBC) 13.358,200 2.95 2,621 95 6.3 22 3.0 22.3 2.62 (VBC) 17.4 37,700 1.90 949 922.6 23 3.0 22.3 + 19.2 2.62 (VBC) 17.4 48,700 2.42 1,616 92 3.9 24 3.022.3 + 19.2 2.49 (VBC) 17.4 51,300 2.31 1,616 94 4.2 25 3.0  5.58 2.62(VBC) 4.4 23,300 2.70 368 86 0.8 26 3.0 22.3 2.78 (VBB) 17.4 10,200 4.54949 72 2.9 27 3.0 22.3 + 19.2 2.64 (VBB) 17.4 9,800 8.10 1,616 81 4.1 283.0 28.2 + 19.2 2.95 (VBC) 11.8 29,000 3.14 1,821 84 4.7 29 3.0 22.32.53 (BC) 17.4 4,100 2.53 923 49 2.6 30 3.0 22.3 + 38.4 2.49 (VBC) 17.447,100 2.40 2,284 93 5.3 31 3.0 22.3 + 67.2 2.49 (VBC) 17.4 50,000 2.983,284 90 8.4 ^(a))M_(n)th = Sty(g)/BuLi (mole) + 57 + MW (CTA) − MW(halogen) ^(b))Styrene added at once to BuLi/solvent in the 1^(st) step.

EXAMPLES 32 to 41

Approaches to dendritic polystyrenes from BuLi, styrene,vinylchlorodimethylsilane (VCD) or vinyl(chloromethyl)dimethylsilane(VCM) in THF at −78° C. M_(n) and M_(w)/M_(n) by GPC in THF vs. PStystandards; BuLi added at once to styrene/solvent in the 1^(st) step; andcommercial grade substrates dried over molecular sieves. See Table 3 forresults.

TABLE 3 BuLi Sty (mmol) M_(w)/M_(n) M_(n)/th.^(a)) Tg Example (mmol)(1^(st) + 2^(nd) steps) CTA (mmol) THF (ml) M_(n) (GPC) (GPC) linear (°C.) Yield (g) 32* 3.04 19.2 + 9.60 2.49 VCD 1 (+9) 3,200 1.61 1,129 513.4 33 3.04 19.2 + 9.60 2.07 VC) 10 5,500 3.22 1,129 68 3.1 34 3.032.5 + 28.8 2.90 VCD 11.3 6,700 2.48 2,272 76 6.7 35 3.0 22.3 2.49 VCD17.4 4,800 2.19 917 71 2.3 36 3.0 22.3 + 19.2 2.90 VCD 17.4 6,500 2.191,584 72 4.2 37 3.04 19.2 2.60 VCM 10 8,400 3.17 841 70 2.3 38* 3.0419.2 2.60 VCM 1 (+9) 2,100 1.70 841 25 2.5 39* 2.04 19.2 + 9.60 2.60 VCM1 (+9) 3,300 1.80 1,143 38 3.2 40 3.0 32.5 2.97 VCM 11.3 9,400 3.041,286 74 3.8 41 3.0 22.3 + 19.2 2.97 VCM 17.4 6,200 2.22 1,598 71 4.4^(a))M_(n)th= Sty(g)/BuLi (mole) + 57 + MW (CTA) − MW (halogen) *In 1 mlTHF + 9 ml PhMe at room temperature.

EXAMPLES 42 to 46

Demonstration of Branched Structure of Polystyrenes Prepared Usingp-Vinylbenzyl Chloride as Chain-Terminating/Branching Agent

Branched structures were confirmed by very low inherent viscosities, low“a”coefficient in the Mark-Houwink equation falling in the range 0.18-0.66 vs. 0.72 for linear polystyrenes and branching factorsapproaching 0.4. See Table 4.

TABLE 4 Characterization of Branching in Dendritic Polystyrenes M_(w)g′^(d) Example IV^(a) LS^(b) SEC^(c) M_(η) ^(c) M_(w),Ls^(e)M_(η),SEC^(e) M_(w)/SEC^(e) gw′^(c) a^(c) Control 0.22 34,500 1.03 0.72(Linear PSty) 42 0.28 88,300^(b) 79,000^(b) 71,100 0.66 0.77 0.72 0.870.66 43 0.19 81,000^(b) 80,000^(b) 63,000 0.48 0.57 0.48 0.63 0.18 440.20 87,800  0.48 45 0.22 83,800  0.56 46 0.28 188,700   0.39^(a)measured in THF via capillary viscometry ^(b)measured in PhMe^(c)SEC viscometry with universal calibration ^(d)g′= ([η]b/{η])_(M) =[η]b/K_(Mb) ^(a) ^(e)a = 0.725, K = 11 × 10⁻⁵ (for linear PSty)

What is claimed is:
 1. A composition of matter comprising a polymerhaving a branch-upon-branch structure and optionally a polymerizableolefinic end group, having the structure:

where B=

wherein: B′=Y,B; m=1 to 100, n=0 to 100, p=0 to 100, n+m+p>2; and ifm >1, then the m insertions are consecutive or not consecutive;A=anionic initiator moiety R; Q is selected from the group consisting ofa covalent bond, R, C(O), and RC(O); Y is selected from the groupconsisting of R, CO₂R, CN, and NR₂; W is CZ═CH₂ or a non-polymerizablemoiety; Z is CN; and R is selected from the group consisting ofunsubstituted and substituted alkyl, vinyl, aryl, aralkyl, alkaryl andorganosilanyl groups, the substituents being the same or different andselected from the group consisting of carboxylic acids, carboxylicester, hydroxyl, alkoxy, primary amino and secondary amino.
 2. Acomposition according to claim 1 wherein A=butyl, and Y=Ph, andQ=C₆H₄CH₂.
 3. A composition of claim 2 wherein W is a non-polymerizablemoiety.
 4. A composition of claim 3 wherein W is H.